Adverse short- and medium-term respiratory effects of work at the World Trade Center (WTC) disaster site have been widely documented in Fire Department of the City of New York (FDNY) first responders and others. Our FDNY team first reported WTC cough syndrome, demonstrated that work-related exposures to the disaster site increased the odds of aerodigestive symptoms up to nine years post-9/11, and showed that the prevalence of physician-diagnosed respiratory conditions, both self-reported and FDNY-physician diagnosed, remained elevated seven to nine years after working at the site. However, in contrast to hundreds of publications about WTC-related lower respiratory conditions, we found only 5 peer-reviewed publications that focused on upper airway disturbance, specifically chronic rhinosinusitis (CRS). In a current cooperative agreement with the National Institute of Occupational Safety and Health, we have been using innovative statistical methods - parametric survival models with change points - to examine whether the relationship between WTC-exposure and new onset obstructive airway disease was stable over the first post-9/11 decade or whether the observed association attenuated over time. Our preliminary results confirm the persistence of the exposure response/gradient for the cumulative incidence of disease for at least the first five years after exposure. We now propose to extend this methodology to address a similar question in CRS incidence, another common respiratory condition associated with exposure to the WTC rescue/recovery effort, with the goal of determining the length of time that exposure response gradients are observed among exposed FDNY firefighters.